1. Field of the Invention
The present invention relates to a laser beam color image display apparatus for controlling laser beams to display a color image on a display screen, and more particularly to a laser beam color image display apparatus for controlling laser beams to display a television color image or the like on a display screen.
2. Description of the Prior Art
Recently, efforts have been directed to the research and development of laser beam color image display apparatus for horizontally and vertically scanning a display screen with intensity-modulated laser beams to display a television color image or the like on the display screen.
Some conventional laser beam color image display apparatus are shown in FIGS. 1, 2, and 3 of the accompanying drawings.
The laser beam color image display apparatus, generally designated by A, shown in FIG. 1, has three laser beam sources, i.e., an argon gas laser beam source 1G for emitting a green laser beam Lg, a krypton gas laser beam source 1R for emitting a red laser beam Lr, and an argon gas laser beam source 1B for emitting a blue laser beam Lb. The laser beam color image display apparatus also includes intensity modulators 2G, 2R, 2B, such for example as acoustooptic intensity modulators, for modulating the intensities of the laser beams from the laser beam sources 1G, 1R, 1B independently of each other, a polygon mirror 3 for deflecting the laser beams horizontally, a galvanometer mirror 4 for deflecting the laser beams vertically, and a projection display screen 5 onto which the laser beams are projected to display a color image thereon.
Lens systems 6, 7 are positioned on both sides of the intensity modulators 2G, 2R, 2B, and lens systems 8, 9 are disposed between the polygon mirror 3 and the galvanometer mirror 4. A reflecting mirror M is positioned to reflect the laser beam that comes from the intensity modulator 2G through the associated lens system 7. Blue- and red-reflecting dichroic mirrors DM.sub.B, DM.sub.R are positioned to reflect the laser beams that come from the intensity modulators 2B, 2R, respectively, through the associated lens systems 7.
The green laser beam Lg, which has a wavelength of 514.5 nm, emitted from the argon gas laser beam source 1G is supplied to the intensity modulator 2G, and modulated in intensity with a green signal component Sg of a video signal that is applied to the intensity modulator 2G. The red laser beam Lr, which has a wavelength of 647.1 nm, emitted from the krypton gas laser beam source 1R is supplied to the intensity modulator 2R, and modulated in intensity with a red signal component Sr of the video signal that is applied to the intensity modulator 2R. The blue laser beam Lb, which has a wavelength of 476.5 nm, emitted from the argon gas laser beam source 1B is supplied to the intensity modulator 2B, and modulated in intensity with a blue signal component Sb of the video signal that is applied to the intensity modulator 2R. Actually, the green, red, and blue laser beams Lg, Lr, Lb to be applied to the intensity modulators 2G, 2R, 2B are separated from the laser beams emitted from the laser beam sources 1G, 1R, 1B by respective color separation dichroic mirrors (not shown). The intensity-modulated laser beams Lg, Lr, Lb are then reflected respectively by the reflecting mirror M, the red-reflecting dichroic mirror DM.sub.R, and the blue-reflecting dichroic mirror DM.sub.B toward the polygon mirror 3.
The polygon mirror 3 comprises a polygonal mirror 13 that is rotated by an actuator 12. The laser beams are horizontally deflected by the rotating polygonal mirror 13, and applied through the lens systems 8, 9 to the galvanometer mirror 4. The galvanometer mirror 4, which is angularly moved reciprocally by an actuator 14, then deflects the laser beams vertically while projecting them onto the display screen 5. Since the laser beams are deflected horizontally by the polygon mirror 3 and vertically by the galvanometer mirror 4, the laser beams applied to the display screen 5 scan the display screen 5 in a raster mode, displaying a color image on the display screen 5 based on the video signal.
For example, the red laser beam Lr of the wavelength of 647.7 nm is produced with an output power of 2 W, the green laser beam Lg of the wavelength of 514.5 nm is produced with an output power of 0.73 W, and the blue laser beam Lb of the wavelength of 476.5 nm is produced with an output power of 0.87 W. As a result, the raster on the display screen 5 provides the standard illuminant C (white light) of 540 lumens.
FIG. 2 shows another conventional laser beam color image display apparatus, generally designated by B. The laser beam color image display apparatus B has an argon gas laser beam source 16 for emitting green and blue laser beams and a dye laser beam source 17 that is excited by the remaining laser beam produced by the argon laser beam source 16 to emit a red laser beam. The laser beam emitted from the argon gas laser beam source 16 is applied to a blue-reflecting dichroic mirror DM.sub.B1 which separates blue laser beams Lb having respective wavelengths of 457.9 nm and 476.5 nm. These separated blue laser beams Lb are supplied to an intensity modulator 2B through a lens system 6. The laser beam that has passed through the blue-reflecting dichroic mirror DM.sub.B1 is then applied to a green-reflecting dichroic mirror DM.sub.G1 which separates a green laser beam Lg having a wavelength of 514.5 nm. The separated green laser beam is supplied to an intensity modulator 2G through a lens system 6. The remaining laser beam that has passed through the green-reflecting dichroic mirror DM.sub.B1 is applied to excite the dye laser beam source 17, which then emits a red laser beam Lr having a wavelength of 612 nm that is reflected by a reflecting mirror M.sub.1 to an intensity modulator 2R through a lens system 6. The blue, green, and red laser beams Lb, Lg, Lr supplied to the intensity modulators 2B, 2G, 2R are modulated in intensity by blue, green, and red signal components Sb, Sg, Sr of a video signal that are applied respectively to the intensity modulators 2B, 2G, 2R. The intensity-modulated laser beams Lb, Lg, Lr are thereafter applied through respective lens systems 7 to a reflecting mirror M.sub.2 and dichroic mirrors DM.sub.G2, DM.sub.B2, by which they are reflected to a light deflector that comprises a polygon mirror, lens systems, a galvanometer mirror identical to those shown in FIG. 1. The laser beams are horizontally and vertically deflected by the light deflector to scan a display screen to display a color image thereon.
FIG. 3 shows still another conventional laser beam color image display apparatus, generally designated by C. The laser beam color image display apparatus C has a single argon-krypton mixed gas laser beam source 19 for emitting a laser beam from which blue, green, and red laser beams Lb, Lg, Lr are separated. Those parts shown in FIG. 3 which correspond to those shown in FIGS. 1 and 2 are denoted by corresponding reference characters.
In the laser beam color image display apparatus C, the laser beam emitted from the argon-krypton mixed gas laser beam source 19 is applied to a blue-reflecting dichroic mirror DM.sub.B1 which separates argon blue laser beams Lb having respective wavelengths of 457.9 nm and 476.5 nm. The laser beam that has passed through the blue-reflecting dichroic mirror DM.sub.B1 is then applied to a green-reflecting dichroic mirror DM.sub.G1 which separates an argon green laser beam Lg having a wavelength of 514.5 nm. The remaining laser beam, i.e., a krypton red laser beam Lr having a wavelength of 647.1 nm, that has passed through the green-reflecting dichroic mirror DM.sub.G1 is reflected by a reflecting mirror M.sub.1. The blue, green, and red laser beams Lb, Lg, Lr are then supplied to respective intensity modulators 2B, 2G, 2R by which they are modulated in intensity by blue, green, and red signal components Sb, Sg, Sr of a video signal that are applied respectively to the intensity modulators 2B, 2G, 2R. The intensity-modulated laser beams Lb, Lg, Lr are thereafter applied through respective lens systems 7 to the dichroic mirrors DM.sub.G2, DM.sub.B2 and the reflecting mirror M.sub.2 by which they are reflected to the polygon mirror 3. The laser beams Lb, Lg, Lr are deflected horizontally by the polygon mirror 3, pass through lens systems 8, 9, and then deflected vertically by the galvanometer mirror 4 to scan the display screen 5 to display a color image thereon.
In the laser beam color image display apparatus shown in FIG. 1, the krypton gas laser beam source 1R cannot produce a red laser beam with a high output power, and the red laser beam Lr of the wavelength of 647.1 nm has a low specific luminosity of 0.12 (see FIG. 4). Therefore, the luminance of the image displayed on the display screen is relatively low and cannot be increased because it is limited by the output power of the red laser beam Lr.
In the laser beam color image display apparatus shown in FIG. 2, since the red laser beam Lr is produced by the dye laser beam source 17 excited by the argon gas laser beam, the image displayed on the display screen is brighter than the image displayed by the laser beam color image display apparatus shown in FIG. 1. More specifically, when the dye laser beam source 17 employs a rhodamine dye as a laser material and is excited by an argon gas laser beam with an output power of 6 W, the dye laser beam source 17 emits a red laser beam having a wavelength of 612 nm with an output power of about 2 W. The red laser beam of the wavelength of 612 nm has a higher specific luminosity of 0.478 (see FIG. 4), which is about four times the specific luminosity of the red laser beam of the wavelength of 647.1 nm. The image displayed on the display screen has a luminance of 650 lumens as a whole. The monochromatic light of the red laser beam of the wavelength of 612 nm is sufficient to cover the red range in the NTSC television system. However, the handling and maintenance of the dye laser beam source 17 is not easy since the laser material is a liquid and has to be circulated as a laminar jet flow within the resonator. Moreover, difficulty has been experienced with dye layers in producing a laser beam in good TEM.sub.00 mode compared with argon and krypton gas lasers. Laser beams in poor mode conditions give rise to energy loss in intensity modulators. The dye laser beam source 17 requires the exciting laser beam source to have an output power capability of 6 W. Therefore, the laser beam color image display apparatus B shown in FIG. 2 cannot easily be reduced in size. Another problem is that the dye in the dye laser beam source 17 must be cooled in the circulation system for increased service life.
The laser beam color image display apparatus C shown in FIG. 8 also poses limitations on the illuminance of the displayed image because the red laser beam is produced by a krypton gas laser and has a wavelength of 647.1 nm.